Condition monitoring of pumps and pump system

ABSTRACT

A method of monitoring the condition of a pump ( 10 ) or at least one component of a system that includes a pump which component or components are not a part of the pump, includes the step of generating a predetermined test condition in the pump or system component or components. During a period in which such a test condition is present, signals indicative of the pump or system component or components are obtained. Wear in the pump bearings, the build-up of deposits in the pump or in pipework forming a part of the pump system can be detected or predicted and corrective action taken before the pump or system fails. By providing a method of monitoring pump or system condition in-situ, it is possible to reduce the likelihood of pump failure in use and the need to carry out over frequent servicing of the pump.

FIELD OF THE INVENTION

The invention relates to condition monitoring of pumps and pump systems,and particularly, but not exclusively to condition monitoring of drypumps.

BACKGROUND OF THE INVENTION

It is known to monitor dry pump condition by observing surges in motortorque or current. This is not, however, an ideal method of predictingpump failure. A pump will usually operate without any noticeable problemwhile deposits gradually build-up in the running clearances. Thisbuild-up usually takes place over a long period of time and eventuallythere will be contact, or rubbing, between two parts. When this happens,the heat generated causes thermal expansion, thus increasing the rubbingand causing further thermal expansion, often leading to seizure and pumpfailure. This contact, or rubbing, can be detected as a surge in motorcurrent. However, the time between detection of a current surge and pumpfailure can be short, and in the case of a dry pump there is usuallyinsufficient time to take action following the detection of a currentsurge.

Pump failure due to seizure is always undesirable, but is even more of aproblem where the pump is being used in a manufacturing process and thepump failure leads to the loss of a batch of product. For example, if avacuum pump fails during the production of semi conductors, typicallythe batch of parts affected has to be rejected, which can be veryexpensive. In order to avoid the problem, pumps can be stripped down andparts replaced or cleaned as part of a planned period maintenancesystem. However, this can result in unnecessary expense as to be safe,the pumps have to be serviced more frequently than is actuallynecessary.

In addition to problems associated with deposits forming in pumps, theefficiency of a pump and the system in which it operates can beadversely affected by the build-up of process by-products in the pumpexhaust, piping connected to the exhaust and/or the pump itself.

Yet another problem with pumps that can lead to pump failure isundetected bearing wear.

BRIEF SUMMARY OF THE INVENTION

It is an object of the invention to at least in part alleviate one ormore of these problems.

The invention provides a method of monitoring the condition of a pump ora component of a system comprising a pump which component is not acomponent of the pump, the method comprising the steps of generating apredetermined test condition in said pump or system component andobtaining signals indicative of a condition of said pump or systemduring a period in which said test condition is present.

The invention also includes apparatus comprising a pump, pump controllerand at least one sensing device for sensing a pump operating parameter,said pump controller being able to control said pump so as toselectively generate a predetermined pump test condition and the or eachsaid sensing device providing signals indicating values of saidparameter when said test condition is generated.

The invention also includes apparatus comprising a pump, a controller,an exhaust conduit extending from said pump, at least one sensing devicefor sensing a condition in said conduit, a connection associated withsaid pump and or conduit for connecting said pump and or conduit with asource of pressurised gas and valving for controlling flow of said gasinto said pump and/or conduit, said controller being able to controlsaid valving to selectively admit said gas into said pump and/or conduitso as to generate a predetermined test condition in said conduit and theor each said sensor providing signals indicative of said condition inthe conduit when said test condition is generated.

In order that the invention may be well understood, embodiments thereof,which are given by way of example only, will now be described withreference to the drawings, in which:

BRIEF SUMMARY OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a pump system; and

FIG. 2 is a flow diagram illustrating a sub-routine carried on a datacarrier for use in implementing a pump monitoring method.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a system is shown in which a pump 10 is connectedto a pipe, or conduit, 12 running from a process chamber 14. The processchamber could be one in which, for example, semi conductors areprocessed. An isolation valve 16 is typically provided in the conduit 12between the pump and the process chamber.

The pump exhaust 18 is connected to a conduit 20 leading to an abatementsystem 22. An abatement system, as is well known to those skilled in theart, is a filtering or treatment system for cleaning the exhaust gases.The pump exhaust 18 and the conduit 20 define a passage for exhaust fromthe pump.

The pump 10 comprises a stator and a rotor (not separately illustrated)and includes an electric motor 24 by which the rotor is driven. In theillustration, the motor is shown outside of the pump. However, it willbe appreciated that this is for ease of illustration and, as is wellknown in the art, the motor may be disposed internally or externally ofthe pump casing and suitable gearing may be provided between the motorand the rotor.

The pump has a controller 26 which will typically comprise a processorand some memory capacity. Typically, the controller will be an integralpart of the pump, but it may instead be provided as a separate unit, orcould be a PC that communicates with the pump via suitable interfaces.

A sensor 30 is associated with the motor and is provided to detect motortorque or the current supplied to the motor. Any suitable sensor may beused. One example is a current clamp probe, which, as will be known tothose skilled in the art, is a probe that can be clamped around a motorlead to perform non-contact current measurements, without interruptingthe circuit under test.

The pump may be connected with a source 34 of coolant that is pumpedthrough the pump in order to cool the pump 10. The source 34 may bemains pressure water, which is directed to a drain once it has passedthrough the pump. Another option is that the source 34 could be a partof a recirculating cooling system that includes a heat transfer devicein which the coolant circulating through the pump is cooled by a heattransfer process. Suitable recirculating cooling systems will be wellknown to those skilled in the art and will not therefore be described infurther detail herein. The system includes some means, typically valvingsuch as an electrically controlled valve 35, which allows the controller26 to control the flow rate of the coolant to the pump.

A pressure sensor 32 is provided in the exhaust conduit 20. Any suitablesensor may be used. One example of a suitable sensor is a diaphragmconnected with a strain gauge or gauges.

In use, the pump would function in the usual way, continuously orintermittently drawing gases from the processing chamber during theprocessing of products therein. During periods in which the pump is notin use, and in some cases even when the pump is in use, diagnostic testsmay be carried out in order to provide data for assessing the conditionof the pump and/or the pump system.

One such test is to determine the condition of the running clearances inthe pump and the bearing condition. In this test, the controller 26 isswitched to a test mode and runs the pump in such a way as to stress thepump. The pump can be stressed in various ways:

-   1) The pump can be run at its normal operating speed, the shaft    speed then reduced for a predetermined period (say three minutes)    followed by an increase above the normal operating speed for a    predetermined period of time (say three minutes). The increase and    decrease in speed could, for example, be 10% above and 10% below the    normal operating speed.-   2) Where the pump is fed with coolant from a source 34, the coolant    flow could be reduced to, for example, 25% of the usual flow rate    for, for example, 10 to 20 minutes. At the end of the reduced flow    period, the flow rate would be restored to its usual level or    possibly increased to a higher level to cause a perturbation of pump    temperature.-   3) Changing the gas flow rates through the pump, by, for example,    increasing the flow rate by as much as 10 to 100 times the rate of    that when the pump is in a usual operating mode. The duration of    this increased throughput could, for example, be between 10 seconds    and one minute-   4) A combination of two or more of methods 1) to 3).

During a period in which the pump is under test, signals indicative ofthe current drawn by the motor 24 are provided by the sensor 30 andcommunicated to the controller 26 where they are stored in the memory. Aprogram operated by the controller can then compare all or some of thedata received from the sensor 30 during the test with pre-programmeddata held in the memory and/or data received during previous tests. Onthe basis of this comparison, a prediction can be made of the remaininglife of the pump before a defined pump condition should occur. If theresult of the test is an indication that the pump may fail within apredetermined period, the pump should be replaced. In this connection,the controller 26 can be equipped in various ways to provide anindication of the result of the test. For example, the controller 26could be linked to an audible device 36 that would provide an audiblemessage indicating the need for pump replacement or that the pump islikely to fail within a specified period. In addition, or as analternative, the controller 26 could be linked to a visual displaydevice 38. The visual display device could be a simple warning light ora screen on which an indication of the test result could be displayed.As a further option, the visual display device 38 could comprise aprinter.

If desired, if the test result indicates certain conditions of the pump,the controller 26 could be configured to render the system inoperableuntil such time as a manual override is operated or resetting takesplace following servicing or replacement of the pump.

Another test can be carried out to determine the condition of the pumpexhaust 18 and/or exhaust conduit 20. In this test, a high purge flow ofgas, for example 100 standard litres minute, is injected into the pump10 or the exhaust conduit 20 upstream of the area to be tested. It willbe understood that the pressure sensor 32 will be positioned relative tothe position or positions at which the gas is injected so as to providesignals suitable for determining the condition of the area to be testedand that it may be appropriate to provide a plurality of such sensors atspaced apart locations in order to provide the desired result. Theinjection period would be relatively short, for example, 10 seconds to 1minute.

In FIG. 1, the gas is shown being injected into the conduit 20 at aposition upstream of the pressure sensor 32 via a pipe 40. Injectioninto the pump is indicated by a dashed line representing a pipe 42. Thepurge gas will typically be nitrogen fed from a source of compressednitrogen 44 but other gases and/or sources could be used instead.Valving 46 is provided in the pipe 40 by means of which the flow of thepurge gas can be controlled. This valving will typically comprise avalve electrically controlled by the pump. In the case of injection intothe pump itself, this test could be a part of method 2) of the stresstest mentioned above and would be carried out when the pump is not inuse. If the purge gas is injected into the exhaust, the test could becarried out when the pump is in use.

During a period in which the pump is under test, signals indicative ofthe pressure in the conduit 20 are provided by the pressure sensor 32and fed to the controller 26 where they are stored in the memory. Thecontroller 26 compares all or some of the received pressure data withthe input gas flow rate and pre-programmed data and/or the data producedby previous tests to determine the level of blockage and/or usefulservice life of the pump exhaust/exhaust conduit 12. The above-describedmethods of providing an indication of the results of a stress test onthe pump can be used to indicate the results of this test and similarly,the controller may be able to render the system inoperable if certainsystem conditions are indicated.

It will be appreciated that the system may be equipped so as to permitthe controller to carry out one or both of the above described tests asdesired and that where only one of the tests is required, theappropriate one of the sensors 30, 32 can be omitted from thearrangement shown in FIG. 1.

In the arrangement described above the tests are performed under thecontrol of the controller 26, which is equipped to analyse the testresults and to provide an indication as to the outcome of the test.However, the pump need not stand-alone and the testing regime can beintegrated into a central system, which allows the test data to beanalysed in connection with test data from other pumps. For thispurpose, the pump may be connected to a network indicated in FIG. 1 bybox 50. The connection to the network 50 may be via the controller 26.However, the pump may be directly connected to the network allowing acentral controller to control the pump without a local controller forthe pump.

The box 50 indicates a network system such as the FabWorks 16 orFabWorks 32 systems marketed by BOC Edwards. These systems permit thedata collected from the sensors 30, 32 to be transmitted to a centralhub where the data can be compared with pre-programmed data, previoustest data from the pump under test and/or test data from other pumps.The FabWorks system can be enabled to provide a secure internetconnection so that the data analysis can be carried out at a central huboperated by, for example, the pump manufacturer. Alternatively, theFabWorks system can be enabled to work on an intranet operated by thepump user. It will be understood that network systems other than theFabworks systems could be used.

The tests should be performed relatively frequent to reduce the risk ofthe tests themselves causing the pump or pump system to fail. Thecontroller 26 and/or central hub may be able to permit manual commandsto initiate the performance of a test. However, to ensure reliablemonitoring of the pump or pump system, it is preferred thatadditionally, or as an alternative, the tests are initiatedautomatically and for this purpose, the controller 26 or a computer ofthe central hub is preferably able to initiate the performance of a testat predetermined intervals. If the test is one that has to be performedwhen the pump is not in use, the controller 26 or computer is able todetermine the use condition of the pump. If the result of theinterrogation is that the pump is not able to be tested, the controlleror computer will preferably be able to interrogate the pump again afterfurther predetermined interval that is less, and preferably much less,than the usual predetermined interval between tests and this process maybe repeated at intervals of decreasing length in the event the pump isstill not in a condition to be tested. The above-described methods ofproviding an indication of the result of a stress test on the pump canalso be used to provide an indication that it was not possible toconduct a scheduled test. Similarly, if it is determined that a test hasnot been conducted sufficiently recently, the controller or hub computermay be able to render the pump or pump system inoperable until some formof manual intervention has taken place.

In an alternative control strategy, the controller or hub computer maybe enabled to detect when the pump has assumed an idle condition, andhaving detected an idle condition, would then check in a memory todetermine when a test was last carried out. If a predetermined intervalhad elapsed since the last test or tests, the controller or hub wouldcause a new test or tests to be initiated. Of course, tests could beinitiated whenever an idle condition is detected, but this would not bea preferred strategy.

One method of detecting the operating condition of the pump, that iswhether the pump is idling or in use, would be to analyse the currentdrawn by the pump motor using signals from the sensor 30, although otherindicators could be used.

It is preferred that the signals from the tests are used in an algorithmto produce an indication of the service life of the pump or pump systembefore a predetermined pump condition is likely to occur and in doingthis, it is expected that the signals from the sensor during the mostrecent test will be compared with signals from previous tests, signalsfrom the sensors of other pumps and/or pre-programmed data. However, inaddition, or as an alternative, the signals from the most recent testmay be analysed in isolation and a determination made on the indicationsfrom those signals. For example, if a threshold value is detected adetermination may be made that servicing or replacement action should betaken. It is expected that such a regime would more likely be applied tothe results of testing on the pump exhaust passage than on results ofthe pump stress test.

It will be appreciated that it is most likely the testing procedureswill be implemented by means of software loaded into the controller or acomputer of the hub and that this, together with the fact that sensorssuch as a current clamp or pressure transducer, can be incorporated withrelative ease, means that the monitoring method can readily be appliedto existing pumps and systems. For example, the software forimplementing the method may be provided on data carrying mediums such asa floppy disc or compact disc. Another option is for the software to bedownloaded via the internet or an intranet. Yet another option is forthe code to be incorporated in a chip which can be substituted for anexisting chip in a controller by itself or more likely as part of areplacement card.

It will be understood that software for implementing the monitoringsystem may take many forms and that many possible routines andalgorithms could be developed. An example of a sub-routine held on adata or carrier 60 in the form of a floppy disc is shown in FIG. 2. Itwill be seen that the sub-routine implements the pump stressing method2) described above and provides for disabling of the pump in the eventthe pump condition is determined as not meeting an ‘OK’ condition. Byway of an example, a determination that the ‘OK’ condition is not metcould be based on the occurrence of two successive tests that indicatethe pump is approaching a failure condition, although of course manyother criteria could be used.

It will be understood that the system and methods described above can bemodified in many ways. For example, transducers may be provided for usein controlling the electrically controlled valving 35, 46 to create afeedback loop by which the valving can be more precisely controlled.Examples of such transducers are temperature sensors for sensing thetemperature of the pump or coolant after it has flowed from the pump, orflow sensors for sensing the coolant or purge gas flow or the gas flowin the conduit.

It will be appreciated that the data collected during the tests may beused to provide an indication of other areas of the pump or system. Forexample, the signals obtained from the conduit 20 may be used to assessthe amount of blockage in the conduit and also of parts of the pump asthere should be a correlation between the two.

It will also be appreciated that the control strategy may be such thatsignals from the sensors are sampled only at predetermined periodsduring testing of the pump or system to ensure that the signals arerepresentative of a period in which the predetermined test condition hasactually been achieved. Another option would be to disregard theobtained signals until such time as a predetermined threshold value isobtained.

1. A method of monitoring the condition of a pump the method comprising the steps of: generating a predetermined test condition in the pump, comprising generating and sustaining for a substantial period of time an abnormal pump speed outside a range of normal pump operation speed whereby the pump is subject to an increased stress as compared with normal operating stresses, thereby causing a reduction in clearance between a rotor and a stator of the pump; and obtaining signals indicative of an amount of the clearance between the rotor and the stator of the pump during a period in which the test condition is present, wherein the signals are derived from a current consumed by a motor driving the rotor of the pump, wherein the reduction in clearance is caused by the steps of causing a predetermined reduction in rotor rotation speed from a selected speed for a predetermined period of time and then causing a predetermined increase in rotor rotation speed above the selected speed for a predetermined period of time.
 2. The method as claimed in claim 1, wherein the pump is equipped to store the signals.
 3. The method as claimed in claim 1, wherein the signals are transmitted to a storage location via a LAN or the internet.
 4. The method as claimed in claim 1, wherein the signals are analyzed to assess the condition of the pump.
 5. The method as claimed in claim 4, wherein the analyzing step comprises comparing the signals with signals obtained during at least one previous predetermined test condition of the pump or system component.
 6. The method as claimed in claim 4, wherein the analyzing step comprises comparing the signals with pre-programmed data.
 7. The method as claimed in claim 4, wherein the analyzing step comprises comparing the signals with signals obtained from at least one other pump or like system component of another system during at least one predetermined test condition of the other pump or system component.
 8. The method as claimed in claim 4, wherein the analyzing step comprises inputting the signals into an algorithm to provide a prediction of pump or system component condition.
 9. The method as claimed in claim 4, wherein the analyzing step comprises inputting the signals into an algorithm to provide a prediction of pump or system component life until a predetermined condition of the pump or system component will occur.
 10. The method as claimed in claim 4, wherein signals indicative of a system component condition are obtained and the analyzing step includes using the signals to predict a condition of the pump or system.
 11. The method as claimed in claim 4, further comprising providing an audible indication of the result of the analyzing step.
 12. The method as claimed in claim 4, further comprising providing a visual indication of the result of the analyzing step.
 13. The method as claimed in claim 4, wherein the pump is automatically closed down if the analyzing step indicates a predetermined condition of the pump.
 14. The method as claimed in claim 1, wherein the pump is able to determine whether the pump is in a condition that permits testing of the pump.
 15. The method as claimed in claim 14, wherein the determining step is performed at predetermined intervals.
 16. Apparatus claimed in claim 1, wherein the sensing device comprises a current sensing device for sensing current consumed by the motor that drives the pump. 